This invention relates to silicone resin coating compositions. More particularly, it relates to silicone coating compositions which provide transparent, abrasion-resistant coatings with improved resistance to ultraviolet radiation. The coatings provided are more weatherable than those previously available.
The substitution of glass with transparent materials which do not shatter has become widespread. For example, transparent glazing made from synthetic organic polymers is now utilized in public transportation vehicles, such as trains, buses and airplanes. Lenses for eyeglass and other optical instruments, as well as glazing for large buildings, also employ shatter resistant transparent plastics. The lighter weight of these plastics in comparison to glass is a further advantage, especially in the transportation industry where the weight of the vehicle is the major factor in its fuel economy.
While transparent plastics provide the major advantage of being more resistant to shattering and lighter than glass, a serious drawback lies in the ease in which these plastics mar and scratch due to everyday contact with abrasives, such as dust, cleaning equipment and/or ordinary weathering. Continuous scratching and marring results in impaired visibility and poor aesthetics, often requiring replacement of the glazing or lens.
Attempts have been made to improve the abrasion resistance of these transparent plastics. For example, coatings formed from mixtures of silica, such as colloidal silica or silica gel, and hydrolyzable silanes in a hydrolysis medium have been developed to impart scratch resistance. U.S. Pat. Nos. 3,708,225, 3,986,997, 3,976,497, 4,368,235 and 4,324,712, describe such compositions and are incorporated herein by reference.
Coating formulations which contain a metal, metal alloy, or metal salt colloidal dispersant such as those of antimony, aluminum, gold, silver, copper, tin, cadmium and indium have been found to provide coatings which are more abrasion resistant than coatings which contain only colloidal silica. Such formulations are described in more detail in U.S. Pat. Nos. 4,442,168, 4,390,373 and 4,500,669, assigned to Swedlow, Inc. The contents of these patents are incorporated herein by reference.
While these coating formulations containing colloidal metal dispersants provide improved mar resistance, there still remains room for improvement. For example, this invention provides coatings with improved weatherability as well as improved mar resistance. These coatings have an added degree of weathering resistance which does not exist in the abrasion resistant coatings provided in the patents assigned to Swedlow, Inc. referred to above.
UV stabilized coating compositions containing silylated UV screening agents have been disclosed by Ashby et al. in U.S. Pat. No. 4,278,804.The compositions of Ashby et al. do not contain the colloidal metals, metal alloys or metal salts utilized in these compositions to enhance mar resistance. It has been discovered that the use of these reactive UV absorbers is not deleterious to the mar resistant properties of the coatings.